The aims of this study are to investigate the genetics of the human integrin collagen receptor alpha 2, beta 1 (a2b1) in order to better understand the association between adhesiveness of human blod platelets to collagens, surface density of the collagen receptor, and inheritance of each of the three alleles of the alpha 2 gene. Platelet a2b1 density will be measured by FACS analysis of platelets labeled with fluorescein-conjugated monoclonal antibodies specific for this receptor.